super class question

[Loren Agular]

Hello, I'm learning about super class.
I am having some problems.
Basically I am asked to determine whether an object of a super class array is of type of subclass.
However i can't use instanceof or getClass.
So i was thinking of using booleans.
So i made a boolean in the subclass that i want and set that to true.
Now i'm trying to pass this new boolean to the superclass however i get this error message: cannot reference grad before supertype constructor has been called
I changed the super class parameters to include the new boolean. However i still get this message.
Please help
Thanks

[Matthew Brown]

You're probably going to have to show us the code.

However, the obvious question is why can't you use instanceof? Because that's what it's for.

[Loren Agular]

I know instanceOf is what it's for but i was told not to use it.
Here is my code:

import java.util.ArrayList;

public class Lab6 {
  
  public static void main(String[] args) {
    ArrayList<Student> students;
    
    students = createStudents();
    printStudents(students);
    
    printDeansList(students);
    printGradStudents(students);
    
    System.out.println("\nEnd of processing.");
  }
  
  public static ArrayList<Student> createStudents() {
    ArrayList<Student> students;
    
    students = new ArrayList<Student>();
    
    students.add(new UndergradStudent(8032, "Casper", 2.78, 2));
    students.add(new GraduateStudent(3044, "Sheena", 3.92, "Natural Language Processing"));
    students.add(new UndergradStudent(6170, "Yolanda", 4.26, 3));
    students.add(new GraduateStudent(1755, "Geordi", 3.58, "Human-Computer Interaction"));
    
    return students;
  }
  
  public static void printStudents(ArrayList<Student> students) {
    Student student;
    
    System.out.println("\nList of all students:\n");
    for (int i = 0; i < students.size(); i++) {
      student = students.get(i);
      System.out.println(i + 1 + ": " + student);
    }
  }
  
  
  public static void printDeansList(ArrayList<Student> students) {
    Student student;
    
    System.out.println("\nDean's honour list:\n");
    for (int i = 0; i < students.size(); i++) {
      student = students.get(i);
      if (student.deansHonourList()) {
        System.out.println(student);
      }
    }
  }
  
  
  public static void printGradStudents(ArrayList<Student> students) {
    Student student;
    boolean GradStudent = false;
    
    System.out.println("\n\nList of graduate students:\n");
    for (int i = 0; i < students.size(); i++) {
      student = students.get(i);

        //GradStudent = GradStudent.isGradStudent();
      
      if (GradStudent) {
        System.out.println(student);
      }
    }
  }
}

class UndergradStudent extends Student{
  
  
  private int year;
  
  
  public UndergradStudent(int number, String name, double gpa, int year) {
    super(number, name, gpa);
    this.year = year;
  }
  
  
  
  
  
// deanHonourList was moved to student class
  
  public String toString() {
    return "Undergraduate: " + super.toString() + ") year: " + year;
  }
}

class GraduateStudent extends Student{
  private String thesis;
  
  
  public GraduateStudent(int number, String name, double gpa, String thesis) {
    
    super(number, name, gpa);
    this.thesis = thesis;
    
  }
  
  
  public boolean deansHonourList() {
    boolean result = false;
    if (getGPA() >= 3.75)
      result = true;
    return result;
  }
  
  
  public String toString() {
    return "Graduate: " + super.toString() + ") thesis: " + thesis;
  }
}

class Student{
  private int number;
  private String name;
  protected double gpa;
  
  public Student(int number, String name, double gpa)
  {
    this.number = number;
    this.name = name;
    this.gpa = gpa;
    
  }
  
  public double getGPA() {
    return gpa;
  }
  
  public String toString()
  {
    return number + " " + name + " (" + gpa;
    
  }
  
  public boolean deansHonourList() {
    boolean result = false;
    if (getGPA() >= 3.50)
      result = true;
    return result;
  }
  
}

basically when i use the printGradStudent() method it should print out only the grad students. However to do this it must be able to differentiate which is a grad student and which is a undergrad student.
The method is not completed yet b/c i had to change it or it wouldn't compile.
I was thiniking of justing making a boolean variable in printGradStudent() and send that to super class (Student) in order to determine if the object is of type GraduateStudent
Thanks